The toolchain part of Go is very interesting (I only know the basics). Go doesn't use GCC, LLVM or other existing compilers. Go's compiler/linker originated from the Plan9 C compiler (that Rob and Ken worked on)[0]. Because of this, it allows you to create binaries for any target platform from any platform you have the Go toolchain on. So from my OSX macbook, I can compile Windows and Linux executables.
When you start diving into it a a bit more, you'll see that Go has it's own ASM language[1] that your code is first compiled into (which then can be translated into specific os/platform asm).
This has it's own ups and downs. Debuggers don't work all that well on Go generated executables (gdb is the closest, even that one isn't all that great). You also don't have the years of optimizations that GCC and LLVM bring to the table. But the Go team has tight control of the tools, which allow for quick compilation and allow them to pick their own direction.